In any polychromatic chromogenic photographic material it is desirable that the dyes so formed should have certain properties. For instance the dyes should be bright in color with very little secondary absorption so that good color reproducibility is obtained. For yellow dyes in particular, color purity is enhanced by ensuring that the absorption maximum of the dye is well separated from that of the magenta dye, and hence yellow dyes that absorb at shorter wavelengths are advantageous. It is also paramount that the formed photographic images should be resistant towards fading by heat, humidity and light. When the dye images are formed in silver halide photographic materials from the combination of oxidized developer and an incorporated coupler, certain restrictions are placed on the properties of the coupler. For instance, the coupler should produce a dye which has the aforementioned desirable properties. Also, the coupler itself must show high efficiency in the dye-forming reaction, must be easily dispersible, must itself be resistant towards the deleterious effects of light, heat and humidity and must have a low propensity to form fog.
In the field of acetanilide-based couplers it is known that incorporating an alkoxy substituent in the 2-position of the aromatic anilide ring can provide a useful hypsochromic shift in image dye hue. In general, however, the light stability of the dyes resulting from such couplers is inferior to that of dyes from couplers with alternative substituents in this position (e.g. chloro). Improvements in light stability can be made through the incorporation of certain stabilizing addenda (e.g. blocked bis-phenols) in the coupler dispersion, but, in general, the alkoxy-substituted couplers remain disadvantaged in image dye stability.
U.S. Pat. Nos. 4,910,126; 5,215,877; 5,219,716; 5,270,156; 5,324,625; 5,336,592; 5,340,703; 5,346,809; 5,376,508; 5,380,639 and 5,382,506 each describe a photographic material comprising a silver emulsion layer containing a substituted acetanilide coupler, disclosing advantages in, for example, raw stock stability and stability to pH fluctuations; lowered fog; color reproducibility and dispersion stability. No evidence is provided in any of these specifications for any improvement in light stability of the yellow dye images by the use of these couplers, nor of any superiority in properties by the selection of a 2-alkoxy acetanilide wherein the alkyl group attached to the oxygen atom is a secondary or tertiary alkyl group.